Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

194
FXUS63 KLOT 092009 CCA
AFDLOT

Area Forecast Discussion...CORRECTED
National Weather Service Chicago/Romeoville, IL
309 PM CDT Tue Jun 9 2026

.KEY MESSAGES...

- A sight chance exists for a few thunderstorms later tonight
  into early Wednesday. While potential is low, it`s possible
  that a storm becomes severe.

- Wednesday and Thursday will be hot and humid with peak heat
  indices in the 90s to locally 100. The hottest conditions are
  favored on Wednesday including up to the Lake Michigan
  shoreline.

- A few rounds of severe thunderstorms may occur in the general
  region Wednesday through Thursday. Thursday continues to look
  like the most concerning day for severe weather locally.

- Friday and Saturday will be dry and noticeably cooler. A
  generally cool and at times wet pattern will develop next
  week.

&&

.DISCUSSION...
Issued at 308 PM CDT Tue Jun 9 2026

Through Tonight...

Our Tuesday was largely quiet and warm through the morning
aside from a few showers around the Chicago metro. As of about 2
PM, temperatures have climbed into the middle 80s and we`re now
seeing a broken cluster of early afternoon thunderstorms south
of I-80 moving east. These are building off of a vort plume tied
to a decaying MCV that`s pushing east across central IL. These
storms are rather garden variety and don`t threaten much outside
of brief downpours and lightning. Coverage is expected to
remain isolated and south of I-80 before eventually moving away
to the east as the vort does.

An upper trough scooting over the High Plains this afternoon
will dig east across the northern CONUS tonight into Thursday.
As the trough works east, it will shunt the Mid-Atlantic high
offshore and open up the region to a southerly mass response
pumping a hot low level air mass and attendant EML plume over
the Midwest beginning tonight. This will set the stage for
several opportunities for severe weather through the end of
Thursday. A NW-SE oriented baroclinic zone on the eastern edge
of the EML plume will progress across the CWA overnight tonight
into early tomorrow morning which some guidance suggests could
trigger a line of late night convection. Some lift will be
needed to overcome the capping inversion and dry EML base and
tap into the 2,000 to 3,000+ Joules of elevated CAPE progged
over the CWA. Much better convective chances exist just west of
the Mississippi where the nose of the LLJ should do well to
trigger thunderstorms, but the kinematic forcing dwindles
quickly with eastward extent across northern IL. Efficient
isentropic upglide through the low levels along and behind the
baroclinic zone may help make up for the lesser forcing. Most
recent CAM guidance does resolve at least pockets of convection
moving northeastward across the CWA after midnight. If storms
develop, the environment will be capable of producing damaging
winds and large hail. Torrential downpours will also be a
concern with PWATs still hanging out above 1.5". In the
forecast, held onto targeted 30-40% PoPs tonight along the
boundary. SPC has maintained a Level 1 of 5 Marginal Risk in
our area through tonight.


Wednesday and Wednesday Night...

With the arrival of that (even warmer) air mass, nighttime
temperatures should only bottom out in the 70s tonight leading
to a scorcher tomorrow with high temperatures forecast in the
lower 90s area-wide, including up to the lakeshore. Dewpoints
into the 70s should push heat indices near or possibly over 100
degrees during the afternoon. Any storms leftover from tonight
should work out of the area during the early morning.

There will be a couple of opportunities for strong to severe
storms tomorrow. Guidance is in good agreement on an MCS firing
up early tomorrow in southern IA/northern MO beneath a shortwave
impulse ejecting northeast out of the Plains. This feature
looks to hold together, if not invigorate, as it tracks toward
the northeast through the morning and across northern IL during
the afternoon. Confidence has grown recently in the presence of
such a feature, but model discrepancies remain in the timing and
strength of this system. The primary window for this potential
would be mid-afternoon into early evening, although some CAMs
still suggest it could approach I-39 by early afternoon. The
afternoon environment will feature little to no capping to over
4,000 Joules of surface-based instability and 25 to 30 kt of
effective shear, modest but certainly ample. Damaging
thunderstorm winds are the biggest concern here, but severe hail
will also be a threat. Can`t rule out a spin up tornado either
with a veering low level wind profile and an unstable 0-3 km
layer.

A much sharper shortwave impulse will track northeast along the
lee of the broader upper trough tomorrow into Thursday. This
will tighten up a frontal boundary across IA and fire up
additional convection during the day west of the Mississippi.
Storms are then expected to translate east across IL later in
the evening and into the night. There remains a plethora of
possible solutions from latest model guidance on how this could
all play out. As the wave gets further displaced to the
northeast, the front will get laid out across southern WI
tomorrow night. With the wonky evolution of the front, storm
motions could vary between eastward and south-southeastward.
Regardless of the exact nature, any storms that do decide to
track across the area will be more than capable of producing
damaging winds and hail. The tornado threat looks generally low
during the night after the low levels stabilize. Will need to
keep a close eye out for any outflow boundaries with storms
tomorrow which could act as a trigger for additional convection
or a track for training storms. With their late morning update,
SPC expanded the Day 2 Level 3 of 5 Enhanced Risk east to
include all of northern Illinois, driven by the potential for
damaging to destructive winds both during the afternoon and into
the night.

Thursday...

Thursday will be another cautiously hot day around the area.
The effective front is progged to get hung up in, or just to,
our north and highs are again forecast in the lower 90s for most
with afternoon heat indices up near 100F.

A potent southern stream wave will develop on the lee of the
Colorado Rockies tomorrow night, propagate northeastward, and
quickly join forces with the larger upper trough over along the
US/Canadian border. The surface response will be a tightly-wound
center of low pressure and associated cold front charging east
through the region Thursday afternoon and evening. The low
center should pass just to our north while the cold front gets
dragged across the CWA, and models agree on a strongly forced
line of convection with the frontal passage during the evening.
This will be a highly dynamic system with 500mb height falls
leading up to Thursday night of nearly 10dam/12hr. The
environment will be highly unstable featuring 3,000 to 4,000+
J/kg of uncapped, surface-based CAPE. Shear will be more
supportive than tomorrow with 35 to 40 kt of effective shear,
still not fantastic but certainly more than supportive of
organized, severe convection, especially when coupled with this
sort of instability. SPC has maintained a level 3 of 5 Enhanced
Risk around the area for Thursday, which still seems very
appropriate as an all hazards severe event could be on the
table.

Friday and Beyond...

Friday will be notably cooler in the wake of the front.
Afternoon highs are forecast in the 70s to near 80. High
pressure working in to our south will bring sunny skies and dry
conditions to Friday. At least the first part of Saturday look
similarly quiet with afternoon temperatures forecast to get back
into the lower 80s, but another upper trough axis is favored to
swing through the Great Lakes with another passing frontal
boundary bringing additional chances for rain and storms later
Saturday into Sunday.

Doom

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1230 PM CDT Tue Jun 9 2026

Key Aviation Messages for the current TAF period:

- Lingering MVFR cigs this afternoon

- Less than 20 percent chance for showers this afternoon, best
  chances around and south of KGYY

- Winds turn to the northeast this evening behind a lake breeze

- A chance for showers and storms with reduced cigs and vis
  around daybreak

- Another chance for storms areawide tomorrow afternoon, some
  may be strong to severe

Winds remain out of the southwest around 10 knots with
occasional gusts under 20 knots. SCT/BKN clouds above 2000 feet
remain over northern Illinois and northwest Indiana. Cloud cover
should scatter out this afternoon, but with lower confidence in
the exact timing, it was decided to maintain a TEMPO for MVFR
cigs through 21Z. There is a weak disturbance over west-central
Illinois that is closely being monitored. As it moves
northeastward, there is a chance for some showers with it, but
the expectation is for these to remain around and south of
KGYY. So while the TAFs for the terminals are dry for the
afternoon, coverage of showers will be monitored in case a AMD
is needed.

As a weak late breeze develops later today, winds are expected
to shift to the east after 00Z. As the strength of the winds
diminishes after sunset, models are suggesting some fog may
develop over Lake Michigan. Some 6SM BR might be possible
overnight, but impacts should be minimal, especially with the
chances for showers and storms.

Toward daybreak, the next disturbance is expected to pass over
northern Illinois providing a 30 to 40 percent chance for
showers and storms. Reduced vis and cigs can be expected with
the strongest embedded cells. Winds will turn to the southwest
behind the rains tomorrow morning with gusts 20 to 25 knots.

Lastly, yet another line of showers and storms is expected
tomorrow afternoon. NAM/HRRR models are showing a mid afternoon
arrival, whereas RAP/HRDRPS shows a much later arrival (possibly
outside the current TAF window). While there is a lot of
uncertainty on the timing of the line, it is looks like this
line could have strong to potentially severe storms with it.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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